Real alchemy: The exciting world of condensed-matter physics!
February 11, 2020 6:24 AM   Subscribe

The new era of polariton condensates (pdf) - "Imagine, if you will, a collection of many photons. Now imagine that they have mass, repulsive interactions, and number conservation. The photons will act like a gas of interacting bosonic atoms, and if cooled below a critical temperature, they will undergo a well-known phase transition: Bose-Einstein condensation. You will have a 'superfluid of light.'" (via)
Now imagine that you can choose the photons' mass. Then, because the critical temperature for Bose-Einstein condensation depends on particle mass and density, you can create the condensed state even at room temperature.

That is not an idle dream. Condensed-matter physicists have a long history of inventing novel quasiparticles, such as massless electrons, particles with fractional charge, and particles with spins detached from their charges. Two decades ago researchers began to engineer hybrid particles of light and matter, called polaritons, that could be used to realize the Bose-Einstein condensates of light described above. Today, the study of polariton condensates has come of age: Researchers have advanced beyond merely demonstrating that they exist to demonstrating ways to harness them in optical devices, including low-threshold lasers, superfluid photonic circuits, and all-optical transistors.


Perhaps no development would be more transformative than fabrication of a polariton-based transistor. Despite decades of optics research, no practical optical transistor yet exists: Current versions are too big to be used in integrated circuits, require very high light intensity, suffer high losses, or have poor on-off ratios. It is not a stretch to say that an efficient optical transistor will someday radically change the nature of optical communications much the way the electronic transistor once changed electronics. Neither is it a stretch to say that that day may be nearly upon us.
The story behind Lightmatter's tech - "Photonic (or optical) computers have long been considered a holy grail for information processing due to the potential for high bandwidth and low power computation. Developing these machines required three decades of technological advancement that Lightmatter is now harnessing to deliver on the promise of highly power-efficient, parallel computation with light."

also btw :P
  • Quantum fluctuations sustain the record superconductor - "When atoms are treated like quantum objects, which are described with a delocalized wave function, the energy landscape is completely reshaped: only one minimum is evident... Somehow, quantum effects get rid of everybody in the mattress but one person, who deforms the mattress only in one single point."
  • Observing localisation in a 2D quasicrystalline optical lattice - "It's well-known that when the potential wells in a crystal get strong enough, its electrons 'localize': instead of having spread-out wavefunctions, they get trapped in specific locations as shown here. This is called 'Anderson localization'. But when a Bose-Einstein condensate localizes, all the atoms get trapped in the *same place* - because they're all in exactly the same state!"
  • Researchers demonstrate optical backflow of light - "If a special superposition of waves, all propagating forward, is constructed, the overall wave can realize what's called 'optical backflow.'"
  • Optical vortex - "An 'optical vortex' is a beam of light that turns like a corkscrew as it moves. It's dark at the center. There's one type of optical vortex for each integer m. You can use an optical vortex to trap atoms! They move along the dark tube at the center of the vortex."
  • Polaritons - "First, when an electron in a crystal is knocked out of place, it leaves a 'hole'. This hole can move around -- and it acts like a positively charged particle! Since electrons are negative and holes are positive, they attract each other! An electron orbiting a hole acts like a hydrogen atom. It's called an 'exciton'. It can move around! But after a while, the electron falls into the hole. Finally, an exciton can attract a photon! They can stick to each other a form a new particle called a 'polariton'! Polaritons are exciting to me because they're made of an electron, an *absence* of an electron, and light."
  • Liquid Light - "Scientists have made *liquid light* by mixing the light with matter."
  • Physicists Discover New Quasiparticle - "There are several more complex quasiparticles: excitons, phonons (particles derived from the vibrations of atoms in a solid), plasmons (particles derived from plasma oscillations), magnons (collective excitations of the electrons' spin structure in a crystal lattice), and polarons (electrons dressed by a phonon cloud)."
  • Making high-temperature superconductivity disappear to understand its origin - "The team believes that something similar to electron-phonon coupling is going on in this case, but instead of phonons, another excitation gets exchanged between electrons. It appears that electrons are interacting through spin fluctuations, which are related to electrons themselves."
  • Scientists discover hidden symmetries, opening new avenues for material design - "Fruchart and Vitelli imagined using this approach to take a particle such as a phonon—essentially a particle of heat—and give it properties that it doesn't usually have. Electrons have a property called 'spin' that is used as a basis for some of the latest high-tech electronics. Phonons don't have a spin, but if scientists could shape the structure of materials to give phonons a 'fake spin', they could potentially use them in phononic devices—similar to electronics, but with different abilities, such as heat control."
  • Physicists Have Identified a Metal That Conducts Electricity But Not Heat - "The team looked at the way that electrons move within vanadium dioxide's crystal lattice, as well as how much heat was being generated. Surprisingly, they found that the thermal conductivity that could be attributed to the electrons in the material was 10 times smaller than that amount predicted by the Wiedemann-Franz Law. The reason for this appears to be the synchronised way that the electrons move through the material."
posted by kliuless (7 comments total) 37 users marked this as a favorite
Wow! So cool. Thanks for posting.
posted by Don.Kinsayder at 8:27 AM on February 11

Thank you! Super interesting topic that I didn't know that I didn't know about. Science and scientists are amazing. Sharing with my junior scientist after school today!
posted by zerobyproxy at 8:49 AM on February 11

Okay, I've got a jar full of photons in my living room now. What's my next step?
posted by delfin at 8:54 AM on February 11 [3 favorites]

Sell before the slump.
posted by storybored at 10:17 AM on February 11 [4 favorites]

Thank you kliuless! this is amazing, will enjoy reading after work.
posted by unearthed at 10:54 AM on February 11

Great, now I know how swapping out bits of glowy colored bits of glass or swapping chunks of crystals make all those Star Trek / Stargate high-tech stuff actually work!
posted by zengargoyle at 11:37 AM on February 11 [1 favorite]

Sadly, my physics degree is from around half a century ago. Of all the links, I had only seen one of them before. And I am not tempted to click on any of the others (totally ignorant of current physics).
posted by baegucb at 9:52 AM on February 12

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